CN115020813A - Lithium ion battery - Google Patents

Abstract

In order to solve the problem of overhigh temperature rise in the charging and discharging processes of the conventional lithium ion battery, the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a nonaqueous electrolyte and a diaphragm, wherein the diaphragm is positioned between the positive electrode and the negative electrode, the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the positive electrode active material comprises lithium cobaltate, the nonaqueous electrolyte comprises a nonaqueous organic solvent, a lithium salt and an additive, and the additive comprises a compound shown in a structural formula 1:

structural formula 1; the lithium ion battery meets the following conditions: h/q m is more than or equal to 0.1 and less than or equal to 15; q is more than or equal to 10 and less than or equal to 50, h is more than or equal to 50 and less than or equal to 130, and m is more than or equal to 0.01 and less than or equal to 3; the lithium ion battery has a maximum surface temperature T in the process of discharging from 2C to 100% DOD at 25 DEG C _max And a minimum surface temperature T _min The following conditions are satisfied: (T) _max ‑T _min )/T _min 100% is less than or equal to 30%. The lithium ion battery provided by the invention has the advantages that the high cycle life and the performance consistency are ensured, and the safety performance is improved.

Description

A lithium-ion battery

technical field

The invention belongs to the technical field of energy storage devices, and in particular relates to a lithium ion battery.

Background technique

Lithium-ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, power vehicles and other fields due to their high specific energy, no memory effect, and long cycle life. High battery voltage and high energy density put forward higher requirements. Lithium cobalt oxide (LCO) is currently the mainstream of 3C lithium battery cathode materials, and the market demand is steadily increasing, so the output of LCO is increasing steadily year by year. With the industrialization of fast-charging (≥2C) and high-voltage (≥4.45V) LCOs, LCOs have been upgraded to a new development platform. However, with the advent of the 5G era, the data transmission speed and processing power of smartphones have been significantly improved compared with the 2G and 3G eras. Application scenarios such as AR, high-definition video, and live broadcasts have accelerated. People have higher and higher requirements for mobile phone performance. The hardware configuration of mobile phones is rapidly iterated, especially with higher requirements for the charging and discharging rate and capacity of 3C digital batteries. But at the same time, the problem of smartphone heating is becoming more and more serious. Mobile phones get hot, freeze and freeze from time to time, and even cause the motherboard to burn out or even explode in severe cases. However, there are very few studies on reducing the temperature rise and the uniformity of temperature distribution of lithium-ion batteries during discharge. Usually, the uneven temperature distribution inside the battery is related to the uneven current distribution inside the battery. The uneven current distribution can easily lead to the battery charging During the discharge process, local overcharge or overdischarge occurs, as well as the inconsistency of the side reaction speed, which leads to the inconsistency of the internal decay rate of the battery; at the same time, reducing the temperature rise of the battery during the high-rate charge and discharge process can also improve the service life of the battery. critical. How to solve the problem of high battery temperature is an urgent problem to be solved to improve the performance of lithium-ion batteries.

SUMMARY OF THE INVENTION

Aiming at the problem that the temperature rise of the existing lithium ion battery is too high during the charging and discharging process, the present invention provides a lithium ion battery.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is as follows:

The present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, the separator is located between the positive electrode and the negative electrode, and the positive electrode includes a positive electrode material layer including a positive electrode active material, so the separator is located between the positive electrode and the negative electrode. The positive electrode active material includes lithium cobalt oxide, the non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive includes a compound shown in structural formula 1:

Structure 1

或

，R₁、R₂各自独立选自H、

、

、

、

或

，R₁和R₂不同时选自H，且X、R₁和R₂中至少含有一个硫原子；wherein, n is 0 or 1, A is selected from C or O, and X is selected from

or

, R ₁ and R ₂ are independently selected from H,

,

,

,

or

, R ₁ and R ₂ are not selected from H at the same time, and X, R ₁ and R ₂ contain at least one sulfur atom;

The lithium-ion battery meets the following conditions:

0.1≤h/q*m≤15;

And 10≤q≤50, 50≤h≤130, 0.01≤m≤3;

Among them, q is the porosity of the diaphragm, and the unit is %;

h is the thickness of the positive electrode material layer, in μm;

m is the mass percentage content of the compound shown in structural formula 1 in the non-aqueous electrolyte, the unit is %;

The maximum surface temperature T _max and the minimum surface temperature T _min of the lithium-ion battery in the process of discharging from 2C to 100% DOD at 25°C satisfy the following conditions:

(T _max -T _min )/T _min * 100%≤30%.

Optionally, the lithium-ion battery meets the following conditions:

0.2≤h/q*m≤6.

Optionally, the porosity q of the separator is 15%-30%.

Optionally, the thickness h of the positive electrode material layer is 60 μm˜110 μm.

Optionally, the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte is 0.1% to 1.0%.

Optionally, the compound shown in the structural formula 1 is selected from at least one of the following compounds:

。

.

Optionally, the charge cut-off voltage of the lithium-ion battery is 4.4V~4.7V.

Optionally, the non-aqueous organic solvent includes ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, propyl At least one of ethyl acetate, ethyl butyrate, methyl acetate, ethyl acetate, fluoroethyl acetate and fluoroether.

Optionally, the additive further includes at least one of cyclic sulfate-based compounds, sultone-based compounds, cyclic carbonate-based compounds, phosphate-based compounds, borate-based compounds, and nitrile-based compounds;

Based on the total mass of the non-aqueous electrolyte as 100%, the additive is added in an amount of 0.01% to 30%.

、

中的至少一种；Optionally, the cyclic sulfate compound is selected from vinyl sulfate, propylene sulfate, vinyl methyl sulfate,

,

at least one of;

The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone;

The cyclic carbonate compounds are selected from vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate or structural formula At least one of the compounds shown in 2,

Structure 2

In the structural formula 2, R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ , and R ₂₆ are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

The phosphate compound is selected from at least one of tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite or compounds shown in structural formula 3:

Structure 3

In the structural formula 3, R ₃₁ , R ₃₂ , and R ₃₂ are each independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si(C _m H _2m+1 ) ₃ , and m is 1～ a natural number of 3, and at least one of R ₃₁ , R ₃₂ and R ₃₃ is an unsaturated hydrocarbon group;

The borate compound is selected from at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate;

The nitrile compound is selected from succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimeliconitrile, suberonitrile, azelonitrile, and sebaconitrile at least one of.

According to the lithium ion battery provided by the present invention, the compound represented by the structural formula 1 is added as an additive in the non-aqueous electrolyte. An interface film is formed on the surface, and the inventors have found through extensive research that in the process of film formation of the compound shown in Structural Formula 1, the content of the compound shown in Structural Formula 1, the porosity of the separator and the thickness of the positive electrode material layer will affect the interface. The film formation quality of the film and the diffusion efficiency of lithium salt ions between the positive and negative electrodes, which in turn lead to the temperature change of the lithium ion battery under charge and discharge, specifically, when the porosity of the separator q, the thickness of the positive electrode material layer h When the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte satisfies the condition 0.1≤h/q*m≤15, the synergistic effect between the separator, the positive electrode material layer and the compound represented by the structural formula 1 can be fully exerted , forming a stable interface film with high ionic conductivity on the surface of the positive and negative electrodes, improving the diffusion efficiency of lithium salts, significantly reducing the heat generation during high-current discharge of lithium-ion batteries While ensuring high cycle life and performance consistency of lithium-ion batteries, the safety performance of lithium-ion batteries is improved.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

An embodiment of the present invention provides a lithium ion battery, including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, the separator is located between the positive electrode and the negative electrode, and the positive electrode includes a positive electrode material layer including a positive electrode active material , the positive active material includes lithium cobalt oxide, the non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive includes a compound shown in structural formula 1;

Structure 1

或

，R₁、R₂各自独立选自H、

、

、

、

或

，R₁和R₂不同时选自H，且X、R₁和R₂中至少含有一个硫原子；wherein, n is 0 or 1, A is selected from C or O, and X is selected from

or

, R ₁ and R ₂ are independently selected from H,

,

,

,

or

, R ₁ and R ₂ are not selected from H at the same time, and X, R ₁ and R ₂ contain at least one sulfur atom;

The lithium-ion battery meets the following conditions:

0.1≤h/q*m≤15;

And 10≤q≤50, 50≤h≤130, 0.01≤m≤3;

Among them, q is the porosity of the diaphragm, and the unit is %;

h is the thickness of the positive electrode material layer, in μm;

m is the mass percentage content of the compound shown in structural formula 1 in the non-aqueous electrolyte, the unit is %;

The maximum surface temperature T _max and the minimum surface temperature T _min of the lithium-ion battery in the process of discharging from 2C to 100% DOD (depth of discharge) at 25°C satisfy the following conditions:

(T _max -T _min )/T _min * 100%≤30%.

The compound represented by the structural formula 1 is added as an additive to the non-aqueous electrolyte. The compound represented by the structural formula 1 is decomposed under electrochemical conditions during the first formation of the battery to form an interface film on the surface of the positive and negative electrodes. The study found that in the process of film formation of the compound shown in Structural Formula 1, the content of the compound shown in Structural Formula 1, the porosity of the separator and the thickness of the positive electrode material layer will affect the film formation quality of the interface film, as well as the lithium salt. The diffusion efficiency of ions between the positive and negative electrodes leads to the temperature change of the lithium-ion battery under charge and discharge. When the mass percentage content m of the compound satisfies the condition of 0.1≤h/q*m≤15, the synergistic effect between the separator, the positive electrode material layer and the compound shown in structural formula 1 can be fully exerted, and high ionic conductivity can be formed on the surface of the positive and negative electrodes. It can stabilize the interface film at a high rate, improve the diffusion efficiency of lithium salts, significantly reduce the heat generation during high-current discharge of lithium-ion batteries, and improve the consistency of temperature rise at various positions of lithium-ion batteries, thus ensuring a higher cycle life of lithium-ion batteries. Improve the safety performance of lithium-ion batteries while maintaining the consistency of performance.

In some embodiments, when n is 0, the compound represented by the structural formula 1 is:

；

;

或

，R₁、R₂各自独立选自H、

、

、

、

或

，R₁和R₂不同时选自H，且X、R₁和R₂中至少含有一个硫原子。wherein, A is selected from C or O, and X is selected from

or

, R ₁ and R ₂ are independently selected from H,

,

,

,

or

, R ₁ and R ₂ are not selected from H at the same time, and X, R ₁ and R ₂ contain at least one sulfur atom.

In some embodiments, when n is 1, the compound represented by the structural formula 1 is:

或

；

or

;

或

，R₁、R₂各自独立选自H、

、

、

、

或

，R₁和R₂不同时选自H，且X、R₁和R₂中至少含有一个硫原子。wherein, A is selected from C or O, and X is selected from

or

, R ₁ and R ₂ are independently selected from H,

,

,

,

or

, R ₁ and R ₂ are not selected from H at the same time, and X, R ₁ and R ₂ contain at least one sulfur atom.

In a preferred embodiment, the lithium-ion battery meets the following conditions:

0.2≤h/q*m≤6.

In a specific embodiment, the porosity q of the separator can be 10%, 13%, 15%, 16%, 18%, 21%, 23%, 24%, 26%, 27%, 29%, 30% %, 32%, 33%, 35%, 39%, 41%, 43%, 46%, 49%, or 50%.

In a preferred embodiment, the porosity q of the separator is 15% to 30%.

If the porosity of the separator is too small, the lithium ions cannot smoothly shuttle between the separators, which will reduce the kinetic performance of the lithium ion battery and increase the battery impedance. In addition, it will lead to worse thermal stability and consistency of the overall battery; if the porosity of the separator is too large, the separator cannot effectively block the shuttle process of harmful impurity substances between the positive and negative electrodes, which will deteriorate the electrochemical performance of the battery. It will cause the positive and negative electrodes to directly contact or be easily pierced by lithium dendrites, resulting in a short circuit.

In a specific embodiment, the thickness h of the positive electrode material layer may be 50 μm, 51 μm, 55 μm, 58 μm, 60 μm, 61 μm, 65 μm, 68 μm, 70 μm, 71 μm, 75 μm, 78 μm, 80 μm, 81 μm, 85 μm, 88 μm, 90 μm , 91μm, 95μm, 98μm, 100μm, 101μm, 105μm, 108μm, 110μm, 111μm, 115μm, 118μm, 120μm, 121μm, 125μm, 128μm or 130μm.

In a preferred embodiment, the thickness h of the positive electrode material layer is 60 μm˜110 μm.

The thicker the positive electrode material layer is, although it is beneficial to improve the energy density of the battery, it also greatly affects the diffusion of lithium ions in the solid phase. The polarization phenomenon during the high-current discharge of the battery causes uneven temperature distribution inside the battery, resulting in inconsistent side reaction rates, which in turn leads to inconsistent internal battery decay rates, which seriously affects the consistency of the battery; if the positive electrode material layer is too low, Then the energy density of the lithium-ion battery is reduced, which is not conducive to commercial application.

In a specific embodiment, the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte may be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.4%, 0.5% , 0.7%, 0.9%, 1.0%, 1.1%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.7%, or 3.0%.

In a preferred embodiment, the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte is 0.1% to 1.0%.

When the content of the compound represented by Structural Formula 1 in the non-aqueous electrolyte is within the above range, it is beneficial to form a high ionic conductivity and stable interface film on the surface of the positive and negative active materials, thereby forming a solid-liquid interface. The fast ion channel promotes the diffusion of lithium ions, significantly reduces the heat generation during high-current discharge of lithium cobalt oxide batteries, improves the consistency of temperature distribution, and reduces the risk of thermal runaway of the battery.

In some embodiments, the compound represented by the structural formula 1 is selected from at least one of the following compounds:

。

.

It should be noted that the above are only the preferred compounds of the present invention, and do not represent limitations of the present invention.

When those skilled in the art know the structural formula of the compound represented by Structural Formula 1, they can know the preparation method of the above compound according to the common knowledge in the field of chemical synthesis. For example: Compound 7 can be made by:

The organic solvents such as sorbitol, dimethyl carbonate, methanol alkaline substance catalyst potassium hydroxide and DMF are placed in the reaction vessel, and after reacting for several hours under heating conditions, a certain amount of oxalic acid is added to adjust the pH to neutrality, and the solution is filtered. After recrystallization, intermediate product 1 can be obtained, and then intermediate product 1, carbonate, thionyl chloride, etc. are esterified under high temperature conditions to obtain intermediate product 2, and then intermediate product 2 is obtained by using an oxidant such as sodium periodate. Compound 7 can be obtained by oxidation.

In some embodiments, the lithium-ion battery is a soft pack battery or a hard case battery.

In a preferred embodiment, the lithium salt is selected from LiPF ₆ , LiBOB, LiDFOB, LiPO ₂ F ₂ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F _{5 )} ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₂ F) ₂ , LiClO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiSO ₂ F, LiTOP (lithium trioxalate phosphate), At least one of LiDODFP (lithium difluorodioxalate phosphate), LiOTFP (lithium tetrafluorooxalate phosphate), and lower aliphatic carboxylate lithium salts.

In some embodiments, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.1 mol/L˜8 mol/L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.5 mol/L to 2.5 mol/L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt may be 0.5 mol/L, 1 mol/L, 1.5 mol/L, 2 mol/L, and 2.5 mol/L.

In some embodiments, the positive active material may further include LiFe _1-x' M'_x' PO ₄ , LiMn _2-y' M _y' O ₄ and LiNi _x Co _y Mn _z M _1-xyz O ₂ At least one of M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, and M is selected from Fe, Co , at least one of Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y ≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1, the positive electrode active material may also be selected from one or more of sulfides, selenides, and halides. More preferably, the positive electrode active material further comprises LiFePO ₄ , LiFe _0.6 Mn _0.4 PO ₄ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , At least one of _0.5 Co _0.2 Mn _0.2 Al _0.1 O ₂ , LiMn ₂ O ₄ , and LiNi _0.8 Co _0.1 Al _0.1 O ₂ .

In a preferred embodiment, the charge cut-off voltage of the lithium-ion battery is 4.4V~4.7V.

In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is formed on the surface of the positive electrode current collector.

The positive electrode current collector is selected from metal materials that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector Choose from aluminum foil.

In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent.

The positive electrode binder includes polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer Copolymers, copolymers of vinylidene fluoride-vinyl fluoride, copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimides, polyethylene and polypropylene and other thermoplastic resins; acrylic resins; methylol sodium cellulose; and at least one of styrene butadiene rubber.

The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

In some embodiments, the negative electrode includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material.

In a preferred embodiment, the negative electrode active material includes at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The carbon-based negative electrode can include graphite, hard carbon, soft carbon, graphene, mesocarbon microspheres, etc.; the silicon-based negative electrode can include silicon material, silicon oxide, silicon-carbon composite material, and silicon alloy material, etc.; tin-based negative electrode It can include tin, tin carbon, tin oxygen, and tin metal compounds; the lithium negative electrode can include metal lithium or lithium alloy. Specifically, the lithium alloy may be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy.

In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode material layer is obtained by blending the negative electrode active material, the negative electrode binder and the negative electrode conductive agent.

The selectable ranges of the negative electrode binder and the negative electrode conductive agent are respectively the same as those of the positive electrode binder and the positive electrode conductive agent, which will not be repeated here.

In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is formed on the surface of the negative electrode current collector.

The negative electrode current collector is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector Selected from copper foil.

In some embodiments, the non-aqueous organic solvent includes at least one of ether-based solvents, nitrile-based solvents, carbonate-based solvents, and carboxylate-based solvents.

In some embodiments, ether solvents include cyclic ethers or chain ethers and their fluorines, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. Can be but not limited to 1,3-dioxolane (DOL), 1,4-dioxoxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2- _CH3 -THF) , at least one of 2-trifluoromethyltetrahydrofuran (2-CF ₃ -THF); the chain ether can be specifically, but not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxy Methane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether. Since chain ethers have high solvability with lithium ions and can improve ion dissociation properties, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. base methane. The ether compounds may be used alone, or two or more of them may be used in any combination and ratio. The amount of ether compound added is not particularly limited, and it is arbitrary within the scope of not significantly destroying the effect of the high-pressure lithium-ion battery of the present invention. When the volume ratio of the non-aqueous solvent is 100%, the volume ratio is usually 1% or more, preferably the volume The volume ratio is 2% or more, more preferably 3% or more by volume, and generally, the volume ratio is 30% or less, preferably 25% or less, and more preferably 20% or less by volume. When two or more ether compounds are used in combination, the total amount of the ether compounds may satisfy the above range. When the addition amount of the ether compound is within the above-mentioned preferable range, the effect of improving the ionic conductivity due to the improvement of the dissociation degree of lithium ions of the chain ether and the reduction of the viscosity can be easily ensured. In addition, when the negative electrode active material is a carbon-based material, co-intercalation due to chain ether and lithium ions can be suppressed, so that the input-output characteristics and charge-discharge rate characteristics can be brought into appropriate ranges.

In some embodiments, the nitrile solvent may be, but not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

In some embodiments, the carbonate-based solvent includes cyclic carbonate or chain carbonate, and the cyclic carbonate may be, but not limited to, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), at least one of butylene carbonate (BC); the chain carbonate can specifically be, but not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), At least one of dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited, and is arbitrary within the scope of not significantly destroying the effect of the lithium ion battery of the present invention, but when one is used alone, the lower limit of its content is relative to the total amount of the solvent of the non-aqueous electrolyte. In general, the volume ratio is 3% or more, preferably 5% or more. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte solution can be avoided, and the large-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery can be easily brought into favorable ranges. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this range, the oxidation/reduction resistance of the non-aqueous electrolyte solution can be improved, thereby contributing to the improvement of stability during high-temperature storage. The content of the chain carbonate is not particularly limited, but is usually 15% or more by volume, preferably 20% or more by volume, and more preferably 25% or more by volume relative to the total solvent of the non-aqueous electrolyte solution. In addition, the volume ratio is usually 90% or less, preferably 85% or less, and more preferably 80% or less by volume. By setting the content of the chain carbonate in the above-mentioned range, the viscosity of the non-aqueous electrolyte solution can be easily brought into an appropriate range, the decrease in ionic conductivity can be suppressed, and the output characteristics of the non-aqueous electrolyte battery can be brought into a favorable range. When two or more types of chain carbonates are used in combination, the total amount of the chain carbonates may satisfy the above range.

In some embodiments, chain carbonates having fluorine atoms (hereinafter abbreviated as "fluorinated chain carbonates") may also be preferably used. The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, preferably 4 or less. When the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms may be bonded to the same carbon or to different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, and the like.

The carboxylate-based solvent includes cyclic carboxylate and/or chain carbonate. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), butyl propionate, At least one of fluoroethyl acetate.

In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone, preferably, in the case of a cyclic sulfone, it usually has 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and in the case of a chain sulfone In the case of a sulfone, it is usually a compound having 2 to 6 carbon atoms, preferably a compound having 2 to 5 carbon atoms. The addition amount of the sulfone solvent is not particularly limited, and is arbitrary within the range that does not significantly destroy the effect of the lithium ion battery of the present invention. Relative to the total amount of the solvent in the non-aqueous electrolyte, the volume ratio is usually 0.3% or more, and the preferred volume ratio is 0.5% or more, more preferably 1% or more by volume, and usually 40% or less by volume, preferably 35% or less by volume, and more preferably 30% or less by volume. When two or more sulfone-based solvents are used in combination, the total amount of the sulfone-based solvents may satisfy the above range. When the addition amount of the sulfone-based solvent is within the above range, a non-aqueous electrolyte solution excellent in high-temperature storage stability tends to be obtained.

In a preferred embodiment, the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate.

In some embodiments, the additive further includes at least one of cyclic sulfate-based compounds, sultone-based compounds, cyclic carbonate-based compounds, phosphate-based compounds, borate-based compounds, and nitrile-based compounds ;

Preferably, based on the total mass of the non-aqueous electrolyte solution as 100%, the additive amount is 0.01% to 30%.

、

中的至少一种；In some embodiments, the cyclic sulfate-based compound is selected from vinyl sulfate, propylene sulfate, vinyl methyl sulfate,

,

at least one of;

The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone;

The cyclic carbonate compounds are selected from vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate or structural formula At least one of the compounds shown in 2,

Structure 2

In the structural formula 2, R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ , and R ₂₆ are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

The phosphate compound is selected from at least one of tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite or compounds shown in structural formula 3:

Structure 3

In the structural formula 3, R ₃₁ , R ₃₂ , and R ₃₂ are each independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si(C _m H _2m+1 ) ₃ , and m is 1～ a natural number of 3, and at least one of R ₃₁ , R ₃₂ and R ₃₃ is an unsaturated hydrocarbon group;

In a preferred embodiment, the phosphate compound represented by the structural formula 3 may be tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, and dipropargyl propyl phosphate Phosphate, Dipropargyl Trifluoromethyl Phosphate, Dipropargyl-2,2,2-Trifluoroethyl Phosphate, Dipropargyl-3,3,3-Trifluoropropyl Phosphate, Dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl triphosphate Fluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl at least one of the base phosphate esters;

The borate compound is selected from at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate;

The nitrile compound is selected from succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimeliconitrile, suberonitrile, azelonitrile, and sebaconitrile at least one of.

In other embodiments, the additives may further include other additives that can improve battery performance: for example, additives to improve battery safety performance, specifically flame retardant additives such as fluorophosphate, cyclophosphazene, or tert-amylbenzene , tert-butylbenzene and other anti-overcharge additives.

It should be noted that, unless otherwise specified, in general, the addition amount of any optional substance in the additive in the non-aqueous electrolyte solution is less than 10%, preferably, the addition amount is 0.1-5%, more preferably , the addition amount is 0.1%~2%. Specifically, the addition amount of any optional substance in the additives may be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2% , 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5 %, 9%, 9.5%, 10%.

In some embodiments, when the additive is selected from fluoroethylene carbonate, based on 100% of the total mass of the non-aqueous electrolyte, the added amount of the fluoroethylene carbonate is 0.05% to 30%.

The present invention will be further illustrated by the following examples.

The compounds involved in the following examples and comparative examples are shown in the following table:

Table 1

Table 2 The design of each parameter of the embodiment and comparative example

Example 1

This embodiment takes the preparation of lithium ion batteries as an example to illustrate the present invention, including the following operation steps:

1) Preparation of non-aqueous electrolyte:

Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC=1:1:1, and then lithium hexafluorophosphate (LiPF ₆ ) was added to mole The concentration is 1 mol/L, and then compound 7 is added. Based on the total weight of the non-aqueous electrolyte as 100%, the mass percentage of compound 7 in the non-aqueous electrolyte is shown in Table 2.

2) Preparation of positive plate:

The cathode active material LiCoO ₂ , the conductive carbon black Super-P and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:3:3, and then dispersed in N-methyl-2-pyrrolidone (NMP ) to obtain a positive electrode slurry. The slurry was evenly coated on both sides of the aluminum foil, dried, calendered and vacuum-dried, and the aluminum lead wires were welded with an ultrasonic welder to obtain a positive electrode plate. The thickness of the positive electrode material layer after vacuum drying is shown in Table 2.

3) Preparation of negative plate:

Mix the negative active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a mass ratio of 94:1:2.5:2.5, and then disperse them in the Ionized water to obtain a negative electrode slurry. Coating the slurry on both sides of the copper foil, drying, calendering and vacuum drying, and welding nickel lead wires with an ultrasonic welder to obtain a negative plate with a thickness of 120-150 μm.

4) Preparation of cells:

A three-layer separator with a thickness of 20 μm is placed between the positive plate and the negative plate. The porosity of the separator is shown in Table 2. Then, the sandwich structure composed of the positive plate, the negative plate and the separator is wound, and then the wound body is pressed After being flattened, it was put into an aluminum foil packaging bag, and vacuum-baked at 85° C. for 48 hours to obtain the cell to be injected.

5) Liquid injection and formation of the cell:

In a glove box with a dew point controlled below -40°C, the non-aqueous electrolyte prepared above was injected into the cell, sealed in vacuum, and kept at rest for 24 hours.

Then the routine formation of the first charge is carried out according to the following steps: 0.1C constant current charging for 45min, 0.2C constant current charging for 30min, 0.5C constant current charging for 75min, secondary vacuum sealing, and then further charging to 4.45V with 0.5C constant current current , and then charged at a constant voltage until the current dropped to 0.02 C. After standing for 5 min, it was discharged to 3.0 V at a constant current of 0.5 C to obtain a LiCoO ₂ /artificial graphite lithium-ion battery.

Embodiments 2 to 25

Examples 2 to 25 are used to illustrate the lithium ion battery disclosed in the present invention and the preparation method thereof, including most of the operation steps in Example 1, and the differences are:

Table 2 shows the negative electrode active material, the thickness of the positive electrode material layer, the porosity of the separator, and the types and mass percentages of additives in the non-aqueous electrolyte used in Examples 2 to 25.

Comparative Example 1~18

Comparative Examples 1 to 18 are used to compare and illustrate the lithium ion battery disclosed in the present invention and its preparation method, including most of the operation steps in Example 1, and the differences are:

The negative electrode active materials, the thickness of the positive electrode material layer, the porosity of the separator, and the types and mass percentages of additives in the non-aqueous electrolyte used in Comparative Examples 1 to 18 are shown in Table 2.

Performance Testing

The following performance tests were performed on the lithium-ion battery prepared above:

1. Battery high current discharge surface temperature range test

Place the lithium-ion battery in a constant temperature environment of 25°C, discharge it to 100% DOD with a current of 2C, and use an infrared camera (model: FLIR-SC325, frame rate 30fps) to monitor the surface of the lithium-ion battery during the discharge process. Temperature, record the maximum temperature value of the lithium ion battery surface as T _max , record the minimum temperature value of the lithium ion battery surface as T _min , and calculate the temperature range percentage through T _max and T _min : temperature range percentage = (T _max - T _min )/T _min * 100%.

2. Cycle performance test

Place the lithium-ion battery in a constant temperature environment of 25°C, charge it to 4.45V with a constant current of 1C, then charge it with a constant voltage until the current drops to 0.02C, and then discharge it to 3.0V with a constant current of 2C, and so on. 800 times, record the first discharge capacity and the last discharge capacity.

Calculate the capacity retention of the cycle as follows:

Battery capacity retention rate (%)=last discharge capacity/first discharge capacity×100%.

(1) The test results obtained from Examples 1 to 14 and Comparative Examples 1 and 5 to 18 are filled in Table 3.

table 3

From the test results of Examples 1 to 14 and Comparative Examples 1 and 5 to 18, it can be seen that lithium cobalt oxide is used as the positive electrode active material, and the compound shown in structural formula 1 is added to the non-aqueous electrolyte. When the thickness h of the material layer and the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte satisfy the preset condition 0.1≤h/q*m≤15, the obtained lithium ion battery has a relatively low battery surface temperature. The difference and high cycle capacity retention rate indicate that the porosity q of the separator, the thickness h of the positive electrode material layer and the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte are. The quality of the interfacial film formed on the surface of the layer has a great influence. The interfacial film obtained under the conditions limited by the above relationship has high stability and good lithium ion diffusion performance. The porosity adjustment of the separator and the positive electrode material The thickness adjustment of the layer can significantly reduce the heat generation of the lithium-ion battery during the high-current discharge process, improve the consistency of the temperature rise of the lithium-ion battery at various positions, and effectively improve the cycle life and safety of the lithium-ion battery.

From the test results of Examples 1 to 14, it can be seen that when the preferred condition of 0.2≤h/q*m≤6 is further satisfied, it is beneficial to further reduce the temperature range of the battery surface of the lithium ion battery and improve the cycle capacity retention rate of the lithium ion battery. , it is speculated that the interfacial film formed by the compound represented by structural formula 1 has better ionic conductivity, thereby effectively reducing the interfacial impedance on the surface of the positive electrode material layer, ensuring the speed of ion diffusion, and avoiding the problem of local overheating.

From the test results of Comparative Examples 5 to 10, it can be seen that even if the porosity q of the separator, the thickness h of the positive electrode material layer and the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte satisfy the preset condition 0.1≤h/q *m≤15 limit, but when the q value, h value or m value does not meet the limit of its range, the lithium ion battery still does not have good performance of avoiding overheating and capacity retention rate, indicating the q value, h value or m value It has a strong correlation in improving the safety performance and cycle performance of lithium-ion batteries. Similarly, when the q value, h value or m value meets the limits of its range, but the h/q*m value does not meet the above preset conditions, the problems of excessive temperature rise and cycle performance degradation of lithium-ion batteries cannot be effectively solved.

(2) The test results obtained in Example 1, Examples 15-17 and Comparative Examples 2-4 are filled in Table 4.

Table 4

From the test results of Example 1, Examples 15-17 and Comparative Examples 2-4, it can be seen that other film-forming additives are used to replace the compounds represented by the structural formula 1 of the present application, such as fluoroethylene carbonate (FEC), 1,3 ,6-hexanetrinitrile (HTCN) or lithium difluorooxalate borate (LiODFB), under the condition of satisfying similar conditions, the performance improvement of lithium ion battery is not as good as the compound shown in structural formula 1 provided by the present invention, indicating that, The 0.1≤h/q*m≤15 provided by the present invention is only for the specific additive of the compound shown in structural formula 1; at the same time, in the battery system provided by the present invention, fluoroethylene carbonate (FEC), 1 ,3,6-hexanetrinitrile (HTCN) or lithium difluorooxalate borate (LiODFB) can further reduce the battery surface temperature range and improve the cycle capacity retention rate. There are certain differences between the compounds shown, and the two have complementary effects in film formation, thereby improving the quality of the interface film on the surface of the positive electrode material layer.

(3) The test results obtained in Example 1 and Examples 18 to 22 are filled in Table 5.

table 5

From the test results of Example 1 and Examples 18 to 22, it can be seen that for different compounds represented by structural formula 1, the porosity q of the separator, the thickness h of the positive electrode material layer and the compound represented by structural formula 1 in the non-aqueous electrolyte When the mass percentage content m meets the preset condition of 0.1≤h/q*m≤15, it plays a similar role, and both have a good improvement effect on the temperature rise problem of lithium-ion batteries, thereby effectively improving the performance of lithium-ion batteries. The cycle life indicates that the relational formula provided by the present invention is applicable to different compounds represented by structural formula 1.

(4) The test results obtained in Example 1 and Examples 23 to 25 are filled in Table 6.

Table 6

From the test results of Example 1 and Examples 23 to 25, it can be seen that when the negative electrode active material is mixed with graphite and silicon oxide in different mass ratios, and the relational formula 0.1≤h/q*m≤15 of the present invention is satisfied. It can also effectively reduce the discharge temperature range of the battery and improve the cycle capacity retention rate. Different anode materials and their combinations.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. a lithium ion battery, is characterized in that, comprises positive electrode, negative electrode, non-aqueous electrolyte and separator, described separator is positioned between described positive electrode and described negative electrode, and described positive electrode comprises the positive electrode material layer that comprises positive electrode active material , the positive active material includes lithium cobalt oxide, the non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive includes a compound shown in structural formula 1:

Structure 1 wherein, n is 0 or 1, A is selected from C or O, and X is selected from

or

, R ₁ and R ₂ are independently selected from H,

,

,

,

or

, R ₁ and R ₂ are not selected from H at the same time, and X, R ₁ and R ₂ contain at least one sulfur atom; The lithium-ion battery meets the following conditions: 0.1≤h/q*m≤15; And 10≤q≤50, 50≤h≤130, 0.01≤m≤3; Among them, q is the porosity of the diaphragm, the unit is %; h is the thickness of the positive electrode material layer, in μm; m is the mass percentage content of the compound shown in structural formula 1 in the non-aqueous electrolyte, the unit is %; The maximum surface temperature T _max and the minimum surface temperature T _min of the lithium-ion battery in the process of discharging from 2C to 100% DOD at 25°C satisfy the following conditions: (T _max -T _min )/T _min * 100%≤30%. 2. The lithium-ion battery according to claim 1, wherein the lithium-ion battery satisfies the following conditions: 0.2≤h/q*m≤6. 3 . The lithium ion battery according to claim 1 , wherein the porosity q of the separator is 15% to 30%. 4 . 4 . The lithium ion battery according to claim 1 , wherein the thickness h of the positive electrode material layer is 60 μm˜110 μm. 5 . 5 . The lithium ion battery according to claim 1 , wherein the mass percentage content m of the compound represented by the structural formula 1 in the non-aqueous electrolyte is 0.1% to 1.0%. 6 . 6. The lithium ion battery according to claim 1, wherein the compound represented by the structural formula 1 is selected from at least one of the following compounds:

. 7 . The lithium ion battery according to claim 1 , wherein the charge cut-off voltage of the lithium ion battery is 4.4V˜4.7V. 8 . 8. The lithium ion battery according to claim 1, wherein the non-aqueous organic solvent comprises ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate , at least one of γ-butyrolactone, propyl propionate, ethyl propionate, ethyl butyrate, methyl acetate, ethyl acetate, ethyl fluoroacetate and fluoroether. 9 . The lithium ion battery according to claim 1 , wherein the additive further comprises cyclic sulfate-based compounds, sultone-based compounds, cyclic carbonate-based compounds, phosphate-based compounds, and borate esters. 10 . At least one of compounds and nitrile compounds; Based on the total mass of the non-aqueous electrolyte as 100%, the additive is added in an amount of 0.01% to 30%. 10. The lithium ion battery according to claim 9, wherein the cyclic sulfate compound is selected from the group consisting of vinyl sulfate, propylene sulfate, vinyl methyl sulfate,

,

at least one of; The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone; The cyclic carbonate compounds are selected from vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate or structural formula At least one of the compounds shown in 2,

Structure 2 In the structural formula 2, R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ , and R ₂₆ are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group; The phosphate compound is selected from at least one of tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite or compounds shown in structural formula 3:

Structure 3 In the structural formula 3, R ₃₁ , R ₃₂ , and R ₃₂ are each independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si(C _m H _2m+1 ) ₃ , and m is 1～ a natural number of 3, and at least one of R ₃₁ , R ₃₂ and R ₃₃ is an unsaturated hydrocarbon group; The borate compound is selected from at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; The nitrile compound is selected from succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimeliconitrile, suberonitrile, azelonitrile, and sebaconitrile at least one of.